The present invention relates to a method for fabricating a semiconductor device, and more particularly, to a method for forming a pattern in a semiconductor device.
As semiconductor devices are highly integrated, a line width of a pattern needs to be decreased. Reduction in the size of photoresist patterns formed by photolithography is also demanded. The main component of photoresist has been changed toward an easier patterning and the exposure technology has been developed toward decreasing the photoresist patterns. However, because of the changes in the main component and the size reduction in photoresist, photoresist patterns may be etched while etching proceeds due to a lack of etching margin. As a result, patterning of etch target layers may be difficult.
In order to solve the above described limitations, an etching margin is secured by interposing a sacrificial hard mask between a patterned etch target layer and a photoresist pattern. A double-layer hard mask structure having a different etching ratio is often considered more effective in securing an etching margin than a single-layer hard mask. In case of using a double-layer sacrificial hard mask structure, material types for hard mask is important, and the types for hard masks are already known.
The possibility of using a sacrificial hard mask structure particularly including an amorphous carbon layer and a tungsten layer is suggested in Korean published patent applications No. 10-2006-0074995 issued to S. K. Lee, et al., entitled “Method For Forming a Deep Contact Hole In Semiconductor Device” and Korean published patent application No. 10-2006-0010932 issued to K. O. Kim, et al., entitled “Method For Fabrication Of Semiconductor Device Using Amorphous Carbon Layer to Sacrificial Hard Mask”. However, for a sacrificial hard mask including an amorphous carbon layer and a tungsten layer, a bottom tungsten layer is usually oxidized when an upper amorphous carbon layer is etched. The oxidation generates a corn-shaped tungsten oxide on the surface of tungsten layer.
FIG. 1A illustrates corn-shaped tungsten oxidation. FIG. 1B illustrates corn-shaped tungsten oxide on the peripheral region. FIG. 1C illustrates a microphotograph of upper tungsten-based hard mask by oxidation on the cell-region. Referring to FIG. 1A, corn-shaped tungsten oxide is generated on a peripheral region. Referring to FIG. 1B, a defect inspection shows that lots of corn-shaped particles on a peripheral region are damaged. In general, the corn-shaped particle is a tungsten oxide. Referring to FIG. 1C, the profile of a tungsten pattern may lack uniformity owing to the corn-shaped tungsten oxide.
As described above, for the case in which a sacrificial hard mask is formed in a double-layer structure including an amorphous carbon and a tungsten layer, the bottom tungsten layer is more likely to be oxidized when the upper amorphous carbon layer is etched. As a result, lots of corn-shaped tungsten oxide is generated on the surface of the tungsten layer. The corn-shaped tungsten oxide may affect subsequent processes and electrical characteristics of devices.